Complete achlorhydria usually follows this operation as performed for peptic ulcer. Should free acid or a pH of 35 be found in the postoperative gastric drainage, an incomplete vagotomy is suspected. Free acid, however, was temporarily secreted in the immediate postoperative period by 14 of these 26 patients as demonstrated by an analysis of their overnight gastric drainage. This occurred despite the demonstration of a satisfactory vagotomy in several of the patients by a negative response to insulin hypoglycemia (Hollander Test). This pa-per elaborates this unexpected finding and considers its possible causes. Consistent achlorhydria after vagotomy and hemigastrectomy has been recorded on several occasions.**** For the most part, these reports were based on late follow up studies. Very few observations similar to those recorded here have been reported on gastric secretions immediately following operation.